Rechargeable lithium-ion batteries are widely used for consumer electronics and exhibit great potential for electrical vehicle and grid-scale energy storage. The first charging process, in which lithium ions and electrons move from cathode to anode, is important for lithium-ion battery operation. When the potential of the anode is below ˜1 V versus Li metal, the organic electrolyte is reduced on the anode surface to form a layer of solid electrolyte interphase (SEI) that is composed of a complex composition of inorganic and organic lithium compounds. In addition, some lithium may be trapped in the electrode upon lithiation. As a result, the first charging process irreversibly consumes a fraction of the lithium ions, giving rise to a net loss of storage capacity. Such first cycle irreversible capacity loss is usually compensated by additional loading of cathode materials in current lithium-ion batteries. However, lithium metal oxide cathodes have much lower specific capacity (mostly less than ˜200 mAh/g) than anodes. Excessive loading of cathode material causes appreciable reduction of battery specific energy and energy density. It is therefore attractive to develop an alternative method that suppresses this loss and consequently increases the 1st cycle Coulombic efficiency.
Addressing first cycle capacity loss is important for the successful commercialization of graphite anodes. With graphite anodes, 5-20% of the lithium from the cathode is typically consumed to form the SEI, corresponding to an appreciable amount of inactivated cathode material. In the past two decades, the 1st cycle Coulombic efficiency of graphite anodes has increased from <80% to 90-95% through optimization of material quality, electrolyte, and additives. Further improvement is likely to result from pre-compensation or prelithiation of the electrodes.
Besides graphite anodes, prelithiation presents exciting opportunities for next generation high capacity anode materials such as Si, Ge, Sn, SiOx, GeOx, SnO2, TiO2 and P, which have a large first cycle capacity loss. For example, Si is a particularly attractive anode material, due to its high specific capacity of ˜4200 mAh/g, excellent material abundance, and well-developed industrial infrastructure for manufacturing. In the past several years, there has been exciting progress in addressing the issues associated with large volume change (>300%) during lithium insertion and extraction by designing nanostructured Si including nanowires and core-shell nanowires, hollow particles and tubes, porous materials, Si/C nanocomposites and by using improved binders. One of the remaining issues for Si anodes is the large capacity loss in the first cycle. The 1st cycle Coulombic efficiency is typically very low, in the range of 50 to 80%, in spite of a few reports with higher values of ˜85%.
The 1st cycle Coulombic efficiency can be improved by prelithiation. Anode prelithiation has been previously achieved by inducing electrical shorting between anode materials and lithium metal foil. It involves the fabrication of a temporary battery, a process which is difficult to scale up. In addition, prelithiation of thick electrode with Li foil is time consuming, as it involves the diffusion of Li ions across the entire anode. Another approach is to use stabilized lithium metal powder (SLMP) to pre-compensate the first cycle irreversible capacity loss of different anode materials, such as graphite and Si-CNT composite. However, SLMP faces many practical challenges yet to be addressed, including large particle size and difficulty to scale up. It is therefore highly desirable to develop alternative microparticles or nanoparticles for prelithiation.